Magnetic storage devices generally store data on a magnetic storage medium through the use of a transducer that writes and reads magnetic data respectively to and from the magnetic storage medium. For example, a disk storage device can include one or more magnetic recording disks that are coaxially mounted on a spindle motor for high-speed rotation. As the disks rotate, one or more transducers, i.e., read and/or write heads, are moved across the surfaces of the disks by an actuator assembly to write and read digital information respectively to and from the magnetic recording disks.
The magnetic storage medium in a magnetic storage device can be organized into one or more data arrays. The surface of a magnetic recording disk in a disk storage system, for example, can be divided into a plurality of concentrically spaced data tracks, generally perpendicular to the radius of the disk. The data tracks on the disk can be further organized into multiple data sectors. Data is often stored within the sectors along the data tracks in the form of a series of magnetic transitions recorded or induced by the head.
Magnetic storage devices often include a control system for accurately and reliably recording and reading data. For example, a disk storage device usually includes a closed-loop servo control system to control the movement of the head across the surface of the magnetic recording disks. To reliably write data to and read data from a desired data track in a magnetic recording disk, the head is positioned over the center of the data track as the track rotates beneath the head. To position the head during one operation, the servo control system first performs a seek function in which the head is moved from its current position to the specified data track. Upon reaching the destination data track, the servo control system performs a tracking function in which the head's position is monitored and adjusted to ensure that the head is following the center of the data track.
The servo control system generally receives a servo information signal from a head indicating the position of the head as the head passes over one or more servo sectors on the disks. The servo control system then processes the servo information signal to determine the current position of the head and the movements to adjust the position of the head, if necessary. Disk storage devices generally employ either dedicated servo systems, in which a separate disk is dedicated to storing servo information, or an embedded servo system in which servo sectors are positioned between data sectors on a single disk. A servo sector may include sector and track identification codes as well as servo burst patterns used to maintain the head's position over the center of the data track.
Given the general desire to store ever-increasing amounts of digital information, designers and manufacturers of magnetic storage devices are continually attempting to increase the bit density of magnetic storage media. In a magnetic recording disk this means increasing the areal density, i.e., both the number of tracks on a disk and the number of bits along a given track. New materials, as well as new recording methods, have helped increase the areal density. For example, bit patterned media, in which a plurality of separated data bits are patterned in the magnetic storage medium, generally allows data bits to be positioned closer together than in a continuous magnetic medium. Servo information, however, must still be included on the disks to provide positioning information for a servo control system. In addition to the complexity of the servo patterning process and subsequent processing cost of the bit patterned media production, the presence of the servo sectors further reduces the area available for recording data.